Ebola virus disease (EVD) is a severe and often fatal illness that affects humans and other primates. It is caused by viruses belonging to the Ebolavirus genus. Understanding the virus’s origin provides insights into how outbreaks begin and are prevented.
The Primary Animal Reservoir
Scientific evidence points to fruit bats as the primary natural hosts for the Ebola virus. These bats, particularly from the Pteropodidae family, carry the virus without developing symptoms. This allows the virus to persist within bat populations as ideal reservoirs.
Researchers have detected Ebola virus antibodies and genetic material in several fruit bat species. While isolating the live virus from bats has been challenging, antibodies indicate past exposure, and viral RNA confirms infection. Bats’ widespread distribution across regions where Ebola outbreaks occur, coupled with their unique immune systems, contribute to their role as carriers.
Pathways of Animal-to-Human Transmission
Transmission of Ebola from its bat reservoir to humans, known as zoonotic spillover, occurs through direct or indirect contact with infected bats or their bodily fluids. Direct contact involves exposure to bat urine, feces, or saliva, particularly in environments like caves where bats roost. People who handle bats, such as hunters or those working in bat-infested areas, face a higher risk.
Indirect transmission can happen when humans come into contact with fruit or other food sources contaminated by bat saliva or feces. Another pathway involves handling and consuming bushmeat, often from animals infected after contact with bats. If bushmeat is not properly cooked or if there is exposure to blood during preparation, the virus can enter the human body.
Other Animals Involved
While fruit bats are the primary reservoir, other animals can become infected with Ebola and play a role in transmission to humans. Non-human primates, such as monkeys, chimpanzees, and gorillas, as well as forest antelopes (duikers), are susceptible to the virus. These animals are not natural reservoirs because they often experience high mortality rates when infected, and the virus does not persist indefinitely within their populations.
These animals act as intermediate hosts, contracting the virus from infected bats or their excretions. Humans can then become infected by handling or consuming the carcasses of these animals, particularly through hunting or butchering practices. While these animals are often associated with outbreaks, they are not the original source but a bridge for transmission from the primary bat reservoir to humans.